1. Field of the Invention
This invention relates generally to plant irrigation systems and more particularly, but not by way of limitation, to a system for irrigating container nursery stock by capillary action.
2. Brief Discussion of the Prior Art
Overhead sprinkler systems have heretofore been employed in nurseries to provide the water required for good growth of container nursery stock. Unfortunately, about ninety percent of the water from an overhead sprinkler system is wasted; that is, the water does not reach the plants in the containers, but falls between the containers on aisles, walkways, or roads adjacent the container production area. In areas of winds and low humidity, up to about sixty percent of the water discharged by an overhead sprinkler system is lost to evaporation. Losses may be even greater with rapidly turning sprinklers that create very small water droplets, thus increasing the droplet surface area subject to evaporation.
To overcome the before-mentioned problems inherent with overhead sprinkler systems, a plurality of individual or "spaghetti" tubes have been employed to water container nursery stock. By watering only the growth medium (soil mix) in the container and not the foliage of the plant, many disease problems are reduced or eliminated and the volume of water required is substantially less than that required when employing an overhead sprinkler system since only the container volume is wetted. Attempts to use individual tubes to water container nursery stock out-of-doors, however, have generally been unsuccessful for several reasons.
A major problem incurred in the use of individual tubes to water container nursery stock is the tremendous gravitational effect inherent within the system, and thus the uneven watering of plants which often occurs. For example, a slope of only a few inches will change the water discharge among a group of tubes from about thirty to about sixty percent.
While the gravitational effect inherent in the use of individual tubes to water container nursery stock can be overcome when using such a system on level greenhouse benches, nursery beds are generally not level due to the need for good surface drainage during periods of heavy rain. In addition, unless the containers are large, the expense and vast number of individual tubes required becomes impractical.
In addition, rodents (e.g., rats, rabbits) and turtles repeatedly bite off, cut or displace the small watering tubes. Since there is no water visible during the irrigation process, if a tube is cut by a rodent or accidentally pulled from a container, the plant is generally lost due to drought before the problem is noticed.
Drip irrigation systems have progressed rapidly during recent years because drip irrigation systems overcome many of the deficiencies and defects prevalent in the overhead sprinkler watering system and in the use of individual or "spaghetti" tubes. A drip irrigation system generally reduces water flight and runoff by about seventy-five percent. However, the difference in the output of water from one emitter to another emitter of a drip irrigation system is a major problem prevalent in the use of the drip irrigation system. To overcome the problem, modern drip irrigation emitters are pressure-compensating. That is, the drip irrigation emitters release a similar quantity of water during a unit of time over a moderate range of water pressure.
Drip irrigation systems also suffer from the detection problem in that when a malfunction occurs, the plant is generally lost due to drought before the defect can be detected and repairs made. Another major problem in the use of a drip irrigation system is that of proper spacing of the emitters. If the plastic pipe is tied to the end containers or stakes at the end of rows when it is hot, upon cooling the containers will be moved or connections pulled apart. On the other hand, if the pipe is tied when it is cool, as it increases in length with heating, it may deflect off the tops of the container. In addition to the problem of maintaining the emitters of a drip irrigation system in the proper location, working among drip irrigation lines poses a problem similar to that encountered when using individual or "spaghetti" tubes to water container nursery stock.
Capillary or sub-irrigation beds have been used for many years in England, New Zealand, and elsewhere for watering nursery stock out-of-doors and, in recent years, for greenhouse container plant production. The basic principle of a capillary bed is the capillary rise of water through the growth medium (i.e., soil mix) due to adhesion and cohesion forces, that is, the attraction of water by various surfaces and small spaces (adhesion) and the attraction of water molecules to each other (cohesion). While the system has worked well on a small scale under the mild climatic conditions of New Zealand and England, capillary or sub-irrigation bed watering systems have shortcomings, which include:
(a) the cost of construction; PA1 (b) the maintenance required, including the periodic replacement of the sand; PA1 (c) transplant shock arising from roots which grow out of the drain holes of the container and into the sand; PA1 (d) increased water loss from the surface of the sand and capillary bed (which can increase water usage to as much as the overhead sprinkler systems) when environmental conditions are appropriate (e.g., low humidity, wind and high temperatures); PA1 (e) germination of weedseed and growth of weeds on the wet surface between the containers; and PA1 (f) algae growth which can quickly become unsightly and limit the useful life of the sand.
Capillary mats, which function on a principle similar to that of capillary or sub-irrigation beds have also been used in the greenhouse and florist industry. In using a capillary mat to water container nursery stock, the entire mat, which is a continuous mat of fabric or foam rubber material, is wetted, much like the capillary or sub-irrigation beds, and water moves capillarily up and into the growth medium in containers placed on the mat. These mats, regardless of composition, are subject to the same shortcomings as the capillary beds described above.
One method for overcoming many of the shortcomings of the before-described systems for watering container nursery stock is the sub-irrigation system disclosed in my U.S. Pat. No. 4,729,189. The sub-irrigation system comprises a thin, flexible sub-irrigation mat upon which containers sit to be irrigated through holes in the bottoms of the containers. Being thin and flexible and having the container sit on the mat, the irrigation outlets defined in the mat remain properly positioned under the containers.
The sub-irrigation mat is also provided with a plurality of cup members upon which the containers sit. Each of the cup members is connected to a channel member adjacent a hole so that water or other irrigating fluids flowing through the hole flows into the interior of the cup member. For example, a collapsible cup device defining the cup member can be positioned at the point where the appropriate center of a container is to be positioned when the container has a center watering hole in its bottom. The size of the collapsible cup device allows for some inaccuracies in placing the container over the respective outlet of the system. The cup also provides a seal with the bottom of the container.
While the sub-irrigation mat disclosed in U.S. Pat. No. 4,729,189 overcomes many of the disadvantages of the prior art watering systems employing capillary mats, capillary beds, drip irrigators, individual or "spaghetti" tubes, as well as overhead sprinklers, the need remains for an improved watering system, particularly a sub-irrigation system, which (a) is simple in construction and operation; (b) is not affected by the wind; and (c) effectively utilizes water in the watering of container nursery stock such that the foliage of such stock remains dry and thereby is less susceptible to disease, while at the same time insuring adequate root growth and substantially reducing root rot diseases which often occur in such container nursery stock. Further, it would be highly desirable if such a watering system would permit one to use capillary action to water the plant while reducing or eliminating algae problems, a problem prevalent with a capillary mat system. It is to such a sub-irrigation system that the present invention is directed.